This invention is directed to a battery monitoring circuit for an electronic wristwatch, and in particular, to a battery monitoring circuit for an electronic wristwatch that prevents an indication of impending battery failure when a temporary, but sudden, load is placed upon the battery by a lamp, alarm or other high impedance device.
In U.S. Pat. No. 3,949,545, filed on Apr. 24, 1975, a battery voltage detecting circuit utilizing the threshold voltage of a field-effect transistor as a battery failure indicator is disclosed. By providing a battery detection circuit, an indication signal can be supplied to the display of an electronic wristwatch to thereby provide an indication to the consumer that the battery is almost dissipated, and hence should be replaced. Battery failure detection circuits of the type disclosed in U.S. Pat. No. 3,949,545 have proved to be extremely convenient and have gained widespread acceptance because of the reliability and convenience provided by same.
It is noted, however, that when a sudden, but temporary, load is placed upon a battery by a lamp or buzzer incorporated in an electronic wristwatch, a sudden, but temporary, drop in the voltage of the battery is often detected by the battery monitoring circuit and, in response thereto, an indication signal representative of imminent battery failure is inadvertently produced. Moreover, once this indication signal is produced, the consumer is likely to replace the battery even though the voltage delivered thereby is immediately returned to a satisfactory level once the temporary load placed upon the battery is removed therefrom. Accordingly, a battery monitoring circuit for an electronic wristwatch that prevents an inadvertent indication of battery failure when a temporary load is placed thereupon is desired.